Directive antenna



June 25, 1946. A; G. KANDOIAN DIRECTIVE ANTENNA Filed July 17, 1944 2 Sheets-Sheet l tut Smwk June25, 1946. A. e. KANDOIAN DIRECTIVE ANTENNA Filed July 17, 1944 2 Sheets-Sheet 2 Patented June 25, 1946 DIRECTIVE ANTENNA Armig G. Kandoian, New York, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application July 17, 1944, Serial N 0. 545,266

1 My invention relates to radio antenna systems. In Patent No. 2,283,897, issued May 26, 1942, to Andrew Alford is disclosed an antenna system producing substantially pure horizontally plane polarized waves. so dimensioning the antenna and energizing it that the vertically polarized components of a wave are substantially neutralized in every direction from the antenna.

The arrangement in the above patent provides a radiating or receiving antenna which has radiant action only for plane polarized waves forming substantially a circular radiant action pattern in the plane of polarization. In other words, the antenna is non-directive.

It has been found that it is possible to retain theprincipal constructional features of the antenna disclosed in the above patent, and at the same time so energize the antenna that radiation therefrom has a maximum value in a single direction. In other words, the antenna is caused to be directive.

Accordingly one of the principal objects of the present invention is to modify the type of antenna disclosed in the patent referred to and generally known as the Alford loop so as to produce therefrom a radiation pattern which is not circular but which is directive in a particular direcradiation from the antenna toward the reflector" iv:

is substantially uniform, and unreflected radiation from the antenna directly outward through the opening of the reflector isreduced to a minimum.

It is a further object of the invention to provide a directional antenna for either transmission or reception, the radiation or reception pattern of .which may be altered by changing the point of connection between the antenna and the trans- Further objects and advantage of the invention will be apparent from the following description of a preferred form of the invention and from the drawings, in which: Fig. 1 is a schematic illustration of an antennasystem as disclosed in the prior art;

Fig. 2 is a vectorialrepresentation, in substance, of the instaneous currents in the arms of the.

antenna of Fig. 1; r I Fig. 3 is a schematic illustration of an antenna i This is accomplished by 7 Claims. (Cl. 250-11) system in accordance with the present invention;

Fig. 4 is a vectorial representation, in substance, of the instantaneous currents in the arms of the antenna of Fig. 3;

Fig. 5 is a schematic illustration showing the antenna of Fig. 3 employed in conjunction with a reflector of the parabolic type.

For the purpose of more clearly understanding the principles of my invention, reference is first made by way of contrast, to Fig. 1, diagrammatically illustrating an antenna I of the type disclosed in Alford Patent No. 2,283,897. This antenna may consist of four radiators 2, 3, 4 and 5 coupled to an R. F. translator 6 over conductors mission line, x

I, 8. Radiators 2, 3, 4 and 5 are shown as curved, and so arranged as to form the periphery of a substantially closed circle. The end of each radiator is bent inwardly, as shown at 9, H), II and I2, so that only the central portions thereof are utilized for radiation. The R. F. translator B is connected to the mid-point l3 of conductors l, 8, and the electrical length of these conductors, which is the diameter of the circle formed by radiators 2, 3, 4 and 5, may be approximately 45, as shown.

Radiators 4 and. 5 are fed. directly from R. F. translator 6 over conductor 1 and radiators 2, 3 are fed over conductor 8 through the transposition shown at M. As a consequence current flows through the radiators in the direction indicated by the arrows. Also, since the current distribution is equal in each of the four arms due to the center connection l3, and is reversed in phase in opposite arms due to the transposition M, the vertical field component will be substantially eliminated in every direction and for every vertical angle with respect to the antenna, as more clearly explained in the aforesaid Alford patent. Furthermore, since at any instant the current in the arms is uniform, the resulting radiation pattern will be substantially circular as indicated at l5.

Fig. 2 illustrates by scalar vectors the produc tion of the circular radiation pattern l5 by antenna I. As an explanation of these vector diagrams, let it be assumed that two linear conductors lying side by side are energized out of phase by currents of equal amplitude. Under these conditions the fields produced by the currents in the two conductors tend to cancel one another, and the resulting radiation is substantially zero.

When the two conductors are drawn apart, however, complete cancellation no longer occurs. This is due to the fact that a certain interval of time is required for the energy radiated from one conductor to reach the other conductor, and by that time the energy which has radiated from the latter has travelled a certain distance into space. The two radiant fields are no longer 180 out of phase, but instead'have a phase difference depending on the distance between the conductors. In thei form of loop illustrated in Fig.1, it has'been assumed, by way of example, that the conductors are displaced apart to such an extent that the energy in the fields produced by the two conductors have a phase displacement of-45.

Referring now to Fig. 2a the radiation from each of the arms 3 and 2 of Fig. lis represented by the scalar vectors R3 "andRz respectively. Since these arms are fed from acommon point l3 equidistant from each arm, the transposition l4 causes the currents in these arms to be 180 out of phase. If these arms3 and 2 were superposed one on the other, or in other words if the ':diameter of the circle formed by the arms.- 2', 3, 4 sand 5-were oi substantially: zero diametergthen :'the radiation from arms 3 and 2 would be represented by the vectors R3 and Rz,i-these-=vectors 1 being of equal length due to the equal amplitude ofthecurrents andextending in oppositedirections due to the 180 differencein' phase. "However, since arms 3-and 2 are separatedat their mid-points by a distance equal to approximately -45 electricaldegreespthe energy radiated from 2 toward 3 is delayed45 with respect to the energy radiated from 3; considering a direction of radiation substantially radially'outwardfrom 3. This phase-retarded radiation-R2 has been shown as R2 in Fig. 2a, phase retardation being indicated by a counter-clockwise rotation of thevector, and

phase advancement by a clockwise rotation. The

total effective radiation isthus the scalar-vector sum of R2 and R3; or R32.

Inthe opposite direction, thephase -of the energy radiated from 3 toward 2 is retardediin phase 45 withrespect to the latter, as indicated in Fig. 2c,'the'eiiective value of the total energy radiated from 2 in said opposite direction being the scalar vector sum of R2 and'Ry, or R23.

Similarly inFigs. 2b and 2d, the total energy radiatedfrom arms 4 and 5 is represented-by the scalar vectors Risuand R54 respectively. It=-will "be noted that or that the efiective value of the energy radiated from the arms of antenna I is substantially equal, producing the circular radiation pattern 15.

According to the present inventin,fthe op -posite arms 2 and 3, and A-and 5, instead of being energized by currents 180 out of phase, arei'enerxgized by currents the phase of which isdetermined by the electrical distance between the point of connection between the R. F. translator. 6 and conductors 1 and B, on one hand, andithe geometrical center of the radiating periphery v on the other. In Fig. 3 the'R. F. translator 6 is point l3, as was the case in Fig. l, but rather, at

I a point l3 which as an illustrative example-is 1 shown as l electrical degrees removed from the center of the periphery The effect of this off-center connection on the radiation characteristics of antenna I is, illus-. trated in the vector diagrams of- Fig. 4. In- Fig.

4a, for example, the vector R3 representingthe normal-radiation from arm 3 corresponding to the vector R3 of Fig. 2a isrotated 15 counterclockwise to assume position Rs'. This is a result" of the fact that current to arm 3 from point 13' takes 15 electrical degrees longer in time to reach arm B than does current from point 13 in Fig. 1, or in other words the phase of the current is retarded 15.

As far as arm 2 is concerned, however, the changing of the input connection from point l3 to point l3 causes the current .to reach arm 2 "more-quickly, due to the shorter distance through which it must travel. This constitutes a advancement in phase of the current to arm 2 overthe original current in Fig. 1. In Fig. 4a, the vector R2 representing the radiation from arm breaching arm 3 with a delay of 45 as shown in Fig. 2a; is nowadvanced in phase 15 (rotated clockwise) 'over its value as shown in Fig. 2a

.to;assume position R2 derived from R3 and R2" is ppreciably shorter than vector R32 of Fig.

'20,, indicating that the effective value of the radiation in Fig. 4a is less than that in Fig. 2a. InFig; 4c lSw'ShOWII' the radiationRz The radiation fromarm.3-:is delayed in'phase 15 in addition to its original delay produced in Fig. 1 by thespacing of the radiating members.

In other words; vector R3 is rotated-counterclockwise to position-R3". The resultant of R2 and R3",- or vector R2 3", indicates that the effective value of the energyradiated isnow greater than that radiated in Fig. l andshown inFig.

InFig; ibthe resulting-vector Ri's 'is'shown to be of approximately the same magnitude as Re'z" inFig, 4a. "Similarly in*'Fig. 4d the vector Raw" approximately equals the '-vector R2'3" :in

- ticularly suited for use in connection with a reconnected to conductors 1, 8 not at the center fiector where it is advantageous to; eliminate radiation directly away from the surface "of the reflector. As shown in Fig. 5, antenna [is-positioned approximately at the center of a parabolic reflector 65' radiation characteristics of the antenna 'aslillus- 16. As a consequ trated by pattern l5 ,'radiation from the antenna is at a maximum in a direction towardthe refiector surface, and at a minimumdire'ctly away therefrom. Both the intensity andthe directional characteristics of the resulting beam; are thus substantially improved.

While I have illustrated the radiating arms 2, 3, 4 and 5 in Fig; 3 as being curved-they. may obviouslyrhave many other shapes snchasthe linear configuration of 5. Likewiseother mean may be substituted, in place ,of the. transposition I 4, for reversing theMp-haseof; .the..currents, in .the ,opposite .arms. Furthermore, .;by substituting a load..=in,:place -of.,the--R.-F. translator 6, the antenna imay-beused for reception instead of transmission.

- While I-have -disclosed-myinventionrzwith respect to a-particular.antennasystem;this showing is made merely by way of'illustration and is not tobe-considered as a limitation on my invening members of each pair being substantially equal and equivalent electrically to less than approximately one-quarter wavelength, two substantially parallel conductors transposed at one point, said conductors respectively joining the radiating members of each of said pairs, a source of energy, and means connecting said source of energy across said conductors at a point between the electrical mid-point of said conductors and the junction of adjacent ends of said conductors respectively with two of said radiating members, whereby current circulates about said periphery in the same sense at all points, and the energy supplied to one radiating member of each of said pairs will be out of phase with the energy supplied to the other member of that pair by an amount substantially equal to twice the electrical distance between mid-point of the conductor joining the member of that pair and the point at which said conductor is connected to said source.

2. A radio antenna system according to claim 1, further comprising a parabolic reflector, said radiating members being positioned substantially symmetrically aboutthe axis of said reflector, with the two radiating members. nearest to the points at which their respective conductors are connected to said source facing the surface of said reflector.

3. A radio antenna system including a plurality of pairs of oppositely-disposed radiating members positioned with ends spaced apart so as to form a substantially closed symmetrical coplanar periphery, each of said radiating members being short with respect to the operating wavelength, the spacing between the mid-points of the radiating members of each pair being substantially equal and equivalent electrically to less than approximately one-quarter wavelength, a plurality of substantially linear conductors of equal length respectively joining the two radiating members of each of said pairs, a source of energy, and means connecting said source of energy across said conductors at a point between the electrical mid-point of said conductors and the junction of adjacent ends of said conductors respectively with two of said radiating members, whereby current circulates about said periphery in the same sense at all points, and the energy supplied to one radiating member of each of said pairs will be out of phase with the energy supplied to the other member of that pair by an amount substantially equal to twice the electrical distance between the mid-point of the conductor joining the members of that pair and the point at which said conductor is connected to said source, to thereby produce maximum radiation in a single direction.

4. A radio antenna system according to claim 3, further comprising a parabolic reflector, said radiating members being positioned substantially symmetrically about the axis of said reflector and arranged so that the maximum effective radiation of said antenna is directed toward the vertex of said parabola.

5. A radio antenna system including four linear radiating members arranged substantially in the form of a square with their ends spaced apart, the distance between opposite members being equal to approximately one-eighth wavelength, two conductors of substantially equal length respectively connecting opposite members, a source of energy, and means connecting said source of energy across said conductors at a point between the electrical mid-point of said conductors and the junction of adjacent ends of said conductors respectively with two of said radiating members, whereby current flows in said radiating members in the same sense at all points, and the current in any member will be out of phase up to a maximum of approximately 45 electrically with the current in the member opposite thereto.

6. A radio antenna system including four oppositely-disposed radiating members arranged in substantially coplanar relation with their ends spaced apart, the distance between the midpoints of opposite members being in the order of one-eighth wavelength, two conductors respectively connecting opposite members, a source of energy, and means connecting said source of energy across said conductors at a point between the electrical mid-point of said conductors and the junction of adjacent ends of said conductors respectively with two of said radiating members, whereby current flows in said radiating members in the same sense at all points, and the current in any one member will be out of phase up to a maximum of approximately 45 electrically with the current in the member opposite to said one member.

7. A radio antenna system including a plurality of pairs of oppositely-disposed radiating members arranged with their ends spaced apart so as to form a substantially closed coplanar periphery, the distance between the mid-points of opposite members being less than approximately onequarter wavelength, a source of energy, and two conductors of unequal length respectively feeding energy from said source to the two radiating members of each pair whereby current flows in said members in the same sense at all points, and the current in any one member will be out of phase up to a maximum of approximately 90 electrically with the current in the member opposite to said one member.

ARMIG G. KANDOIAN. 

